Jenson Button's former boss Nick Fry claimed he was "mystified" by Button's decision to leave Brawn GP, now Mercedes GP, and sign with McLaren.

Button signed the deal with his new team earlier this week, confirming speculation that he was unable to agree on the terms of a contract extension with Brawn. In a cutting reproach, Fry said only time would tell if Button's decision was correct.

"There is bravery and there is stupidity and we will only find out which it is next year," Fry told The Mirror. "We believe we made Jenson a good offer - one that was significantly more than he is being paid at McLaren. Everyone knows we have enormous respect for Jenson. He's an amazing racing driver but we are all mystified by this decision."

However, Fry confirmed Button's decision had likely revolved around personal ambition rather than money. "We think he has been badly advised and had his head turned by McLaren's glitzy headquarters," Fry added. "We think it's an emotional decision rather than a financial one based on hard dollars."